# std::log10(std::valarray)

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< cpp‎ | numeric‎ | valarray

Defined in header `<valarray>` |  |
template< class T > valarray<T> log10( const valarray<T>& va ); |  |

For each element in va computes common (base 10) logarithm of the value of the element.

### Parameters

va | - | value array to apply the operation to

### Return value

Value array containing common logarithms of the values in va.

### Notes

Unqualified function (log10) is used to perform the computation. If such function is not available, std::log10 is used due to argument-dependent lookup.

The function can be implemented with the return type different from std::valarray. In this case, the replacement type has the following properties:

  - All const member functions of std::valarray are provided.
  - std::valarray, std::slice_array, std::gslice_array, std::mask_array and std::indirect_array can be constructed from the replacement type.
  - For every function taking a const std::valarray<T>& except `begin()` and `end()`(since C++11), identical functions taking the replacement types shall be added;
  - For every function taking two const std::valarray<T>& arguments, identical functions taking every combination of const std::valarray<T>& and replacement types shall be added.
  - The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

### Possible implementation

    template<class T>
    valarray<T> log10(const valarray<T>& va)
    {
        valarray<T> other = va;
        for (T& i : other)
            i = log10(i);

        return other; // proxy object may be returned
    }

### Example

Run this code

    #include <cmath>
    #include <iomanip>
    #include <iostream>
    #include <valarray>

    void show(char const* title, const std::valarray<float>& va)
    {
        std::cout << title << " : " << std::right;
        for (float x : va)
            std::cout << std::setw(6) << x;
        std::cout << '\n';
    }

    int main()
    {
        const std::valarray<float> n{-2.f, -1.f, 0.f, 1.f, 2.f, 3.f, INFINITY};
        const std::valarray<float> pow10{std::pow(10.f, n)};
        const std::valarray<float> log10_pow10{std::log10(pow10)};

        show("n      ", n);
        show("10ⁿ    ", pow10);
        show("lg(10ⁿ)", log10_pow10);
    }

Output:

    n       :     -2    -1     0     1     2     3   inf
    10ⁿ     :   0.01   0.1     1    10   100  1000   inf
    lg(10ⁿ) :     -2    -1     0     1     2     3   inf

### See also

log(std::valarray) | applies the function std::log to each element of valarray (function template)
log10log10flog10l (C++11)(C++11) | computes common (base 10) logarithm (\({\small\log_{10}{x}}\)log10(x)) (function)
log10(std::complex) | complex common logarithm with the branch cuts along the negative real axis (function template)

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